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FSYNC(2) FreeBSD System Calls Manual FSYNC(2)
NAMEfdatasync,fsync -- synchronise changes to a file
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS#include <unistd.h>
intfdatasync(intfd);
intfsync(intfd);
DESCRIPTION
The fsync() system call causes all modified data and attributes of the
file referenced by the file descriptor fd to be moved to a permanent
storage device. This normally results in all in-core modified copies of
buffers for the associated file to be written to a disk.
The fdatasync() system call causes all modified data of fd to be moved to
a permanent storage device. Unlike fsync(), the system call does not
guarantee that file attributes or metadata necessary to access the file
are committed to the permanent storage.
The fsync() system call should be used by programs that require a file to
be in a known state, for example, in building a simple transaction facil-
ity. If the file metadata has already been committed, using fdatasync()
can be more efficient than fsync().
Both fdatasync() and fsync() calls are cancellation points.
RETURN VALUES
The fsync() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The fsync() and fdatasync() calls fail if:
[EBADF] The fd argument is not a valid descriptor.
[EINVAL] The fd argument refers to a socket, not to a file.
[EIO] An I/O error occurred while reading from or writing to
the file system.
SEE ALSOfsync(1), sync(2), syncer(4), sync(8)HISTORY
The fsync() system call appeared in 4.2BSD. The fdatasync() system call
appeared in FreeBSD 11.1.
BUGS
The fdatasync() system call currently does not guarantee that enqueued
aio(4) requests for the file referenced by fd are completed before the
syscall returns.
FreeBSD 11.2 February 6, 2018 FreeBSD 11.2